This application is entitled to the benefit of, and incorporates by reference, essential subject matter disclosed in Swedish Patent Application No. 0201933-9 filed on Jun. 20, 2002.
The present invention relates to a method and a device for cleaning of crankcase gas that is produced during operation of an internal combustion engine used for propelling a vehicle.
Cleaning of crankcase gas requires a cleaning device that can remove effectively the utmost small particles, solid and/or liquid, present in suspended form in the crankcase gas. In recent years centrifugal separators of different kinds have been suggested for such cleaning, and different methods have been suggested for driving of a centrifugal separator used for this purpose. Thus, it has been suggested that a centrifugal separator would be driven mechanically by means of one of the ordinary shafts of the combustion engine, e.g. the crank shaft or the cam shaft (see for instance U.S. Pat. No. 5,954,035). Another suggestion has been that a centrifugal separator would be driven by means of an electrical motor (see for instance WO 01/36103). Even another suggestion has been that a fluid, gas or liquid, would be pressurised by means of the combustion engine and be used for driving a turbine of one kind or another, coupled to a centrifugal rotor for cleaning of crankcase gas (see for instance WO 99/56883).
One starting point in connection with use of a centrifugal separator for cleaning of crankcase gas, that has been produced by an internal combustion engine carried by a vehicle, is that the energy for driving the centrifugal separator should be derived from the combustion engine, either directly or indirectly through a source of energy of some kind, e.g. a generator or an accumulator for electric current or a compressor or a pressure vessel containing compressed air.
This is not completely without problems, however, as a combustion engine is being loaded to different degrees during its operation not only for propelling of the vehicle but also for energizing of various auxiliary equipment on board the vehicle. The supply of energy from a source of energy of the said kind is limited and, above all, the source of energy may be so heavily loaded in certain situations for the vehicle that further withdrawal of power is not possible or acceptable, e.g. for safety reasons.
A main object of the present invention is to provide a method and a device for cleaning of crankcase gas from an internal combustion engine that is arranged for propelling a vehicle, enabling minimization and /or optimization of the effect and energy requirement for the cleaning.
This object can be achieved according to the invention by means of a device including
a centrifugal separator having a centrifugal rotor that is arranged for mounting on the vehicle and for cleaning of said crankcase gas,
an electrical motor, that for its operation is connectable to a source of current available on the vehicle and that is arranged for rotation of the centrifugal rotor, and
equipment for changing the cleaning efficiency of the centrifugal separator, including a control equipment arranged for changing the rotational speed of the electrical motor and, thereby, of the centrifugal rotor during maintained operation of the combustion engine.
By means of a device of this kind the crankcase gas cleaning may be performed in an optimum way, as need comes up for such cleaning, by use of a smallest possible amount of energy. Hereby, also unnecessary wear of different parts of the device, such as bearings and the like, may be avoided. The crankcase gas cleaning may also, periodically, be interrupted completely, although the combustion engine is maintained in operation. The invention is based on an understanding that the crankcase gas cleaning need not have the same efficiency all the time the combustion engine is used and also that the cleaning efficiency of a centrifugal separator can be controlled by changing of the rotational speed of the centrifugal rotor.
The controlling of the rotational speed of the electrical driving motor and, thereby, of the centrifugal rotor may be performed in many different ways, among other things depending upon the type of electrical motor that is used. For instance, already previously known technology, involving frequency conversion, may be used for controlling of the rotational speed of the electrical motor. In a most simple case the controlling may be performed, however, by means of one or more relays of a conventional kind. In a relay of this kind an input circuit may be arranged to be influenced by data intended for changing of the cleaning efficiency of the centrifugal separator, and an output circuit may be arranged to change the rotational speed of the electrical motor in dependence of such data.
As to the required input data for the controlling here in question, the device according to the invention is preferably connectable to a source of information that is available on the vehicle and arranged for delivery of data relevant to an existing or upcoming need for cleaning of crankcase gas produced by the combustion engine. Thus, the control equipment preferably is adapted to be influenced by data from said source of information in a way such that the rotational speed of the centrifugal rotor is adapted, continuously or stepwise, to said need of crankcase gas cleaning. However, sometimes an extremely large need of energy may come up for some other operation on the vehicle, which has a higher priority than the crankcase gas cleaning, and during a certain period of time an accurate control of the kind just mentioned may therefore have to be interrupted. During a period time of this kind it may be necessary to interrupt the crankcase gas cleaning completely or, alternatively, to reduce it to an extent that can be predetermined and pre-programmed for various operational situations for the vehicle. Said control equipment of the device according to the invention, thus, sometimes may have to be influenced in a way different than that happening when the control equipment is to accurately adapt the cleaning efficiency of the centrifugal separator to an actually prevailing cleaning need.
On a modern vehicle of the category large lorries and working machines there is normally a computer network installed. One previously known computer network of this kind is called CAN-bus (CAN=Controller Area Network). In this computer network, which preferably includes a vehicle computer and is coupled to many different sensors placed in different parts of the vehicle and in the combustion engine, there are a lot of data available concerning various functions and conditions prevailing on the vehicle. Examples of data which may be available are:
the present engine speed
the present load on the engine
the load on the engine as desired by the driver of the vehicle (present pressure on the accelerator pedal of the vehicle)
the engine temperature
the ambient air temperature
the speed of the vehicle
the total operational time of the engine since the engine was new
the driving distance of the vehicle since the engine was new
operational time since the engine was last started
Of course, many other data are available in a network of this kind depending upon which components are present on the vehicle. By means of a vehicle computer connected with the network various data may be combined and converted into control signals of various kinds for controlling of various functions on board the vehicle, e.g. signals for controlling of the cleaning of crankcase gas according to the invention.
In a preferred embodiment of the device according to the invention its equipment for changing the cleaning efficiency of the centrifugal separator may comprise a decoding- or selection device, that is adapted to receive or choose only certain ones of several data available in a source of information of this kind, said control equipment being adapted to be actuated by such received or chosen data and, in turn, to change the rotational speed of the electrical motor in dependence thereof.
Irrespective of whether a computer network of the aforementioned kind is available or not the cleaning device in an advantageous embodiment of the invention is preferably connectable to a sensor that is arranged to sense an actual change of the amount of crankcase gas being produced by the combustion engine. Alternatively or in addition thereto, the cleaning device may be connectable to a sensor, that is arranged to sense a change of the amount of particles, solid or liquid, present in the crankcase gas to be cleaned, e.g. crankcase gas being on its way between the crankcase of the combustion engine and the centrifugal separator. In an arrangement of this kind the cleaning efficiency of the centrifugal separator may be adapted to a cleaning need that can be expressed by a formula including values for both the amount of particles present in the crankcase gas on its way to be cleaned and the actual flow of such crankcase gas.
In addition to a device of the kind described above the invention includes a method of cleaning crankcase gas according to the subsequent claims.